Method and apparatus for forming modular sockets using flexible interconnects and resulting structures

ABSTRACT

A modular bare die socket assembly for attaching a plurality of miniature semiconductor dice to a substrate. The socket assembly is comprised of a plurality of two-sided plates joined vertically in a horizontal stack, wherein each plate has a die socket for the removable insertion of a bare semiconductor die. A multi-layer interconnect lead tape has a plurality of lithographically formed leads bent on one end to form nodes for attachment to bond pads on the removably inserted semiconductor die, and having opposing ends connectable to the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of application Ser. No.10/158,979, filed May 30, 2002, pending, which is a continuation ofapplication Ser. No. 09/876,805, filed Jun. 7, 2001, now U.S. Pat. No.6,478,627, issued Nov. 12, 2002, which is a continuation of applicationSer. No. 09/487,935, filed Jan. 20, 2000, now U.S. Pat. No. 6,319,065B1, issued Nov. 20, 2001, which is a continuation of application Ser.No. 09/072,260, filed May 4, 1998, now U.S. Pat. No. 6,089,920, issuedJul. 18, 2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to methods and apparatus forelectrically connecting semiconductor devices to circuit boards. Moreparticularly, the invention relates to a socket into which one or morebare semiconductor die may be inserted for connection to a circuit boardwithout wire bonding of the contact pads of the semiconductor die.

[0004] 2. State of the Art

[0005] The assembly of a semiconductor device from a leadframe andsemiconductor die ordinarily includes bonding of the die to a paddle ofthe leadframe, and wire bonding bond pads on the die to inner leads i.e.lead fingers of the leadframe. The inner leads, semiconductor die, andbond wires are then encapsulated, and extraneous parts of the leadframeexcised, forming outer leads for connection to a substrate such as aprinted wiring board (PWB).

[0006] The interconnection of such packaged integrated circuits (IC)with circuit board traces has advanced from simple soldering of packageleads to the use of mechanical sockets, also variably known asconnectors, couplers, receptacles and carriers. The use of sockets wasspurred by the desire for a way to easily connect and disconnect apackaged semiconductor die from a test circuit, leading tozero-insertion-force (ZIF), and low-insertion-force (LIF) apparatus.Examples of such are found in U.S. Pat. No. 5,208,529 of Tsurishima etal., U.S. Pat. No. 4,381,130 of Sprenkle, U.S. Pat. No. 4,397,512 ofBarraire et al., U.S. Pat. No. 4,889,499 of Sochor, U.S. Pat. No.5,244,403 of Smith et al., U.S. Pat. No. 4,266,840 of Seidler, U.S. Pat.No. 3,573,617 of Randolph, U.S. Pat. No. 4,527,850 of Carter, U.S. Pat.No. 5,358,421 of Petersen, U.S. Pat. No. 5,466,169 of Lai, U.S. Pat. No.5,489,854 of Buck et al., U.S. Pat. No. 5,609,489 of Bickford et al.,U.S. Pat. No. 5,266,833 of Capps, U.S. Pat. No. 4,995,825 of Korsunskyet al., U.S. Pat. Nos. 4,710,134 and 5,209,675 of Korsunsky, U.S. Pat.No. 5,020,998 of Ikeya et al., U.S. Pat. No. 5,628,635 of Ikeya, U.S.Pat. No. 4,314,736 of Demnianiuk, U.S. Pat. No. 4,391,408 of Hanlon etal., and U.S. Pat. No. 4,461,525 of Griffin.

[0007] New technology has enabled the manufacture of very smallhigh-speed semiconductor dice having large numbers of closely spacedbond pads. However, wire bonding of such semiconductor dice is difficulton a production scale. In addition, the very fine wires are relativelylengthy and have a very fine pitch, leading to electronic noise.

[0008] In order to meet space demands, much effort has been expended indeveloping apparatus for stack-mounting of packaged dies on a substratein either a horizontal or vertical configuration. For example,vertically oriented semiconductor packages having leads directlyconnected to circuit board traces are shown in U.S. Pat. No. 5,444,304of Hara et al., U.S. Pat. No. 5,450,289 of Kweon et al., U.S. Pat. No.5,451,815 of Taniguchi et al., U.S. Pat. No. 5,592,019 of Ueda et al.,U.S. Pat. No. 5,619,067 of Sua et al., U.S. Pat. No. 5,635,760 ofIshikawa, U.S. Pat. No. 5,644,161 of Burns, U.S. Pat. No. 5,668,409 ofGaul, and U.S. Reissue Pat. Re. 34,794 of Farnworth.

[0009] However, none of the above patents relates to the socketinterconnection of a bare i.e. unpackaged semiconductor die to asubstrate such as a circuit board.

[0010] Sockets also exist for connecting daughter circuit boards to amother board, as shown in U.S. Pat. No. 5,256,078 of Lwee et al. andU.S. Pat. No. 4,781,612 of Thrush. U.S. Pat. Nos. 4,501,461 and Re.28,171 of Anhalt show connectors for connecting a socket to a circuitboard, and wiring to an electronic apparatus, respectively.

[0011] U.S. Pat. No. 5,593,927 of Farnworth et al. discloses asemiconductor die having an added protective layer and traces, and whichis insertable into a multi-die socket. The conductive edges of thesemiconductor die are connected through an edge “connector” to circuitboard traces. The number of insertable semiconductor dice is limited bythe number of semiconductor die compartments in the socket, and usingfewer dice is a waste of space.

SUMMARY OF THE INVENTION

[0012] A modular bare die socket is provided by which any number of bare(unpackaged) semiconductor dice having bond pads along the edge of onemajor side may be interconnected with a substrate in a densely packedarrangement. The socket is particularly applicable to high speed, e.g.300 MHZ dice of small size or those dice of even faster speeds.

[0013] The socket comprises a plurality of plates which have asemiconductor die slot structure for aligning and holding a bare die ordice in a vertical orientation, and interconnect structure for aligningand retaining a multi-layer lead tape in contact with conductive bondpads of an inserted die. The interconnect lead tapes have outer endswhich are joined to conductive traces on a substrate such as a printedwiring board (PWB).

[0014] Each lead tape includes a node portion which is forced against abond pad to make resilient contact therewith. Various means forproviding the contact force include a resilient lead tape, anelastomeric layer or member biasing the lead tape, or a noded arm of theplate, to which the lead tape is fixed.

[0015] A multi-layer interconnect lead tape may be formed from a singlelayer of polymeric film upon which a pattern of fine pitch electricallyconductive leads is formed. Methods known in the art for forming leadframes, including negative or positive photoresist optical lithography,may be used to form the lead tape. The lead tape may be shaped underpressure to the desired configuration.

[0016] The plates with intervening interconnect lead tapes are bondedtogether with adhesive or other means to form a permanent structure.

[0017] The plates are formed of an electrically insulative material andmay be identical. Each plate has “left side structure” and “right sidestructure” which work together with the opposing structure of adjacentplates to achieve the desired alignment and retaining of thesemiconductor die and the lead tape for effective interconnection.

[0018] Any number of plates may be joined to accommodate the desirednumber of bare semiconductor dice. Assembly is easily and quicklyaccomplished. If desired, end plates having structure on only one sidemay be used to cap the ends of the socket.

[0019] Thus, a socket is formed as a dense stack of semiconductordie-retaining plates by which the footprint per semiconductor die ismuch reduced.

[0020] The modular socket is low in cost and effectively provides thedesired interconnection. A short interconnect lead distance is achieved,leading to reduced noise. The impedance may be matched up to the contactor semiconductor die.

[0021] The primary use of the modular bare semiconductor die socket isintended to be for permanent attachment to circuit boards of electronicequipment where die replacement will rarely be required. Although thesocket may be used in a test stand for temporarily connecting diceduring testing, new testing techniques performed at the wafer scalegenerally obviate the necessity for such later tests.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0022] The invention is illustrated in the following figures, whereinthe elements are not necessarily shown to scale:

[0023]FIG. 1 is a perspective view of a modular socket of the invention;

[0024]FIG. 2 is a perspective view of partially assembled modules of amodular socket of the invention;

[0025]FIG. 3 is a cross-sectional edge view of a portion of a modularsocket of the invention, as generally taken along line 3-3 of FIG. 1 andhaving an exploded portion;

[0026]FIG. 4 is a perspective view of a multi-layer lead tape useful ina modular bare die socket of the invention;

[0027]FIG. 5 is a plan view of a multi-layer lead tape useful in amodular bare die socket of the invention;

[0028]FIG. 5A is a plan view of another embodiment of a multi-layer leadtape of a modular bare die socket of the invention;

[0029]FIG. 6 is a perspective view of a further embodiment of amulti-layer lead tape of a modular bare semiconductor die socket of theinvention;

[0030]FIG. 7 is a perspective view of partially assembled modules of afurther embodiment of a modular bare semiconductor die socket of theinvention;

[0031]FIG. 8 is a perspective view of partially assembled modules of anadditional embodiment of a modular bare semiconductor die socket of theinvention;

[0032]FIG. 9 is a cross-sectional edge view of a portion of a furtherembodiment of a modular bare semiconductor die socket of the invention,as taken along line 3-3 of FIG. 1, and having an exploded portion;

[0033]FIG. 10 is a cross-sectional edge view of a portion of anotherembodiment of a modular bare semiconductor die socket of the invention,as taken along line 3-3 of FIG. 1;

[0034]FIG. 11 is a view of a semiconductor die for use in the modularbare semiconductor die socket of FIG. 10;

[0035]FIG. 12 is a view of the semiconductor die of FIG. 11 used in themodular bare semiconductor die socket of FIG. 10; and

[0036]FIG. 13 is a view of an alternative embodiment of thesemiconductor die and modular bare semiconductor die socket of FIG. 12illustrating a modified lead tape.

DETAILED DESCRIPTION OF THE INVENTION

[0037] As depicted in drawing FIG. 1, a modular bare die socket 10 ofthe invention comprises a plurality of modules 12A, 12B and 12C formedof plates 14A, 14B, 14C, and 14D which are stacked perpendicular to asubstrate 16. A bare (unpackaged) semiconductor die 18 with conductivebond pads (not visible) near one edge on a major surface 20 thereof,e.g. the “active surface” may be inserted as shown into a die slot 22and have its bond pads interconnected to conductive traces (not visible)on the surface 24 of the substrate 16.

[0038] The internal structures of plates 14C and 14D are depicted indrawing FIG. 2. Each of the plates 14A, 14B, 14C and 14D has a firstside 26 and an opposing second side 28. The plates have first ends 30having die slots 22, and second ends 32 having lead slots 44 throughwhich lead tapes pass.

[0039] In these figures, the first side 26 is taken as the left side ofeach plate and the second side 28 is taken as the right side. Theregular plates 14A, 14B and 14C have structure on both sides 26, 28 andmay be the exclusive plates of the socket 10. The structure provides foraccommodating bare semiconductor dice 18 of a particular size, numberand spacing of bond pads, etc. and for electrically interconnecting thesemiconductor dice 18 to a substrate 16. Typically, all regular plates14A, 14B, 14C of a bare die socket 10 are identical but in some casesmay differ to accommodate semiconductor dice of different size, bond padconfiguration, etc. within different modules 12A, 12B, 12C, etc. of asocket.

[0040] Alternatively, one or two end plates 14D may be used to cap anynumber of intervening regular plates 14A, 14B and 14C. In contrast tothe regular plates 14A, 14B and 14C, such end plates 14D havecooperating structure on one side only, i.e. the internal side, and maysimply have a flat exterior side which in drawing FIGS. 1, 2 and 3 isthe second side 28. Specifically designed end plates 14D may be used oneither, neither or both ends of the socket 10, and have structure on oneside to complement the facing side of the adjacent regular plate 14A,14B, 14C.

[0041] The structure of the second side 28 of the regular plates 14A,14B and 14C is shown as including an upwardly opening die slot 22 with aside wall 34, edge walls 38, and stop end wall 36 of lower beam 40.Lower beam 40 has an exposed surface 42 which is one side of aninterconnect lead slot 44. The lower beam 40 is shown as having a width41 exceeding width 46 for accommodating means for accurate alignment andretention of a multi-layer interconnect lead tape 50, not shown indrawing FIG. 2 but to be described later in relation to drawing FIGS. 3through 6.

[0042] The first sides 26 of plates 14A, 14B, 14C and 14D are as shownwith respect to end plate 14D. In this embodiment, first side 26 islargely flat with a recess 48 for accommodating portions of theinterconnect lead tape. Recess 48 has a width 60 which is shown toapproximate the width 46 of the die slot 22, and has a depth 62 which issufficient to take up the lead tape 50 when it is compliantly moved intothe recess upon insertion of a semiconductor die 18 into die slot 22.

[0043] The module 12C including the first side of plate 14D and thesecond side of plate 14C has alignment posts 52 and matching holes 54for alignment of the plates 14C, 14D to each other. Also shown arealignment/retention posts 56 and matching holes 58 for (a) aligning andretaining an interconnect lead tape 50 in the module, and for (b)aligning the plates 14C, 14D with each other. The posts 52, 56 andmatching holes 54, 58 together comprise a module alignment system.

[0044] Mating portions of adjacent plates are joined by adhesivefollowing installation of the lead tape 50 on alignment/retention posts56. Each of the posts 52, 56 is inserted into holes 54, 58 so that allof the plates 14A, 14B, 14C and 14D are precisely aligned with eachother to form a monolithic socket 10. In drawing FIG. 3, all of theregular plates 14A, 14B, and 14C are identical.

[0045] In the views of drawing FIGS. 3 through 5, a multi-layerinterconnect lead tape 50 is shown as comprised of a first insulativelayer 64, with a second layer 66 of conductive leads 70 fixed to it. Theinsulative layer 64 may be formed of a film of polymeric material suchas polyimide, polyimide siloxane, or polyester. A conductive layer 66,typically of metal, is formed on the insulative layer 64 in the form ofindividual leads 70A, 70B, 70C, etc. Methods well-known in the industryfor producing multi-layer lead frames may be used for forming the finepitch leads 70 on the insulative layer 64. Thus, for example, the leads70 may be formed by combining metal deposition with optical lithographyusing either a positive or negative photoresist process. Any methodcapable of providing fine pitch leads 70 on the first layer 64 of thelead tape 50 may be used.

[0046] The lead tape 50 has an upper portion 72 which is configured witha total width 76 of leads 70 which generally spans the semiconductor die18, but will be less than width 46 of die slot 22 (see FIG. 2). A lowerportion 74 has a greater width 78 which may correspond generally towidth dimension 41 of the lower beam 40 (see FIG. 2). Alignmentapertures 80, 82 are formed in the lower portion 74 to be coaxial alongaxes 84, 86, respectively, with alignment/retention posts 56.

[0047] The upper portion 72 includes lead portions which contact thebond pads 90 of the dice. The lower portion 74 includes lead portionswhich are joined to substrate 16.

[0048] In the embodiments of drawing FIGS. 3, 4, 5 and 5A, the lead tape50 is shown as being formed in the general shape of the letter “S.” Acontact node 88 is formed in each lead 70 in the upper portion 72 byforming the upper portion as a bend. The node 88 is configured to bepushed away by contact with a bond pad 90 of a semiconductor die. Theresistance to bending of the lead produces compression therebetween andenables consistent electrical contact with the bond pad 90 of asemiconductor die. Where the surfaces of the bond pads 90 of thesemiconductor die 18 are essentially coplanar, contact between the bondpads 90 and the leads 70 is maintained. The compressive force betweenthe semiconductor die 18 and the leads 70 is dependent upon theparticular material of insulative layer 64 and its thickness, thethickness and material of conductive layer 66, and lead displacementfrom the unbiased position which results from die insertion. Typically,the insulative layer 64 may vary in thickness from about 12 to about 300μm. The preferred thickness of the conductive layer 66 is about 25 toabout 75 μm. The total thickness of the combined first and second layersof the lead tape 50 is preferred to be from about 75 μm to about 100 μm.

[0049] The lower ends 92 of leads 70 are shown as bent to a nearlyhorizontal position for surface attachment to a substrate 16.

[0050] The lower ends 92 are shown as having the insulative layer 64removed to provide a metal surface for attachment by soldering or othermethod to a substrate 16.

[0051] In a variation of the lead tape 50 shown in drawing FIG. 5A, theupper ends of the leads 70, i.e. the leads in the upper portion 72, mayhave both the insulative layer 64 and conductive layer 66 removedbetween the leads, thereby singulating them. Each lead 70 retains bothlayers 64, 66 for retaining a required resistance to bending in eachlead. Thus, each lead is independently compliant with respect to aninserted semiconductor die 18 to retain conductive contact with a bondpad 90 on the semiconductor die 18.

[0052] An alternative embodiment of the interconnect lead tape 50 isdepicted in drawing FIG. 6. The lower ends 92 of leads 70 are bent inthe opposite direction from drawing FIGS. 5 and 5A and in addition, theinsulative layer 64 is not removed from the lower ends 92.

[0053] The lead tape 50 may be bent to the desired shape by a suitablestamping tool or the like, wherein the “at-rest” shape is uniform fromtape to tape.

[0054] The placement of the module components, i.e. the die slot 22,lower beam 40, interconnect lead slot 44, and recess 48 may be varied inthe longitudinal direction 94 (see FIG. 3) of the plates, and may beapportioned in any convenient way between the first side 26 of one plateand the facing second side 28 of an adjacent plate.

[0055] Turning now to drawing FIGS. 7, 8 and 9, several otherembodiments of the modular socket 10 are illustrated. As depicted indrawing FIG. 7, a plurality of regular plates 14A, 14B and 14C and anend plate 14D, the plates providing for an interconnect lead tape 50using a compressible elastomeric member 96 to bias the tape to the bondpads 90 of the semiconductor die 18. The elastomeric member may beformed of silicone foam, solid silicone that has been perforated, or lowdurometer hardness silicone which is attached to the tape by adhesive.The elastomeric member 96 may be variably shaped as a narrow strip 96Awith limited biasing strength to a more general coverage 96B withgreater biasing strength. Both are illustrated in drawing FIG. 9. Thenarrow strip 96A is intended to be used in the module design of drawingFIG. 7, and the high coverage member 96B may be used in the moduleembodiment of drawing FIG. 8, wherein sufficient space is provided inthe interconnect lead slot 44 for the elastomeric member. Preferably,the elastomeric member 96A or 96B comprises a single continuous unitextending across all of the leads 70. Alternatively, a series ofelastomeric members 96 may be arrayed on the tape 50.

[0056] Referring to drawing FIG. 10, illustrated is another form of theinvention, in which the compliant member of a module 12 comprises aprojecting portion 100 of the plate 14. The projecting portion 100 maybe in the form of a ledge, as shown in the figure, and includes alongitudinal ridge 102 within a recess 48 in the side 26. A multi-layerinterconnect lead tape is attached, e.g. by adhesive to the projectingportion 100 and ridge 102. The resulting node 104 in the lead tape 50 isforced away by an inserted die 18 and forcibly abuts the bond pads onthe die surface 20. The force holding the leads 70 against inserted bondpads 90 of a semiconductor die 18 will depend upon the distance 106 fromthe node 104 to the attachment point 108 of the ridge 102. In order toprovide the desired effect, the polymeric material of the plate 14 andprojecting portion 100 is selected in combination with distance 106 andledge thickness 110. In this embodiment, it is unnecessary for the leadtape 50 to be aligned and retained on alignment posts.

[0057] Where a bare semiconductor die 18 has two rows of bond pads 90,illustrated in drawing FIG. 11 as first row 112 and second row 114, thelead tape 50 of the modular socket 10 may be adapted for lead contactwith both rows. A lead tape 50 for providing contact with two rows 112,114 of bond pads 90 is shown in drawing FIG. 12. The tape 50 comprisesthree layers including a first insulative layer 64, a second conductivelayer 66 for contacting the first row 112 of bond pads 90, and a thirdconductive layer 68 for contacting the second row 114 of bond pads onthe die 18. The first and second layers 64, 66 are terminated atlocations 116, 118, respectively, between the first and second rows 112,114 of bond pads. An elastomeric member 96C such as a foam is attachedto the third layer 68 and abuts the recess wall 120. The member 96C iscompressed by insertion of the semiconductor die 18 into the socket andretains forced contact between the leads and bond pads.

[0058] As shown in drawing FIG. 13, the first (insulative polymer) layer64 may alternatively be provided with holes 122 through which individualleads 70 of the third (conductive) layer 68 are preinserted for contactwith the second row 114 of bond pads 90.

[0059] The foregoing delineates several examples of the use of amulti-layer lead tape with means for contacting the bond pads of a baredie. Other types of biasing apparatus may be used for maintainingcontact between interconnect leads 70 and the bond pads 90 of asemiconductor die 18, including mechanical springs suitable for theminiature devices.

[0060] The plates 14A, 14B, 14C, 14D, etc. may be molded of a suitableinsulative polymeric material, examples of which include polyethersulfone, polyether ether ketone (PEEK), or polyphenylene sulfide.

[0061] Following assembly of the modular socket 10 and attachment to asubstrate 16, the modular socket, or portions thereof, may be“glob-topped” with insulative sealant material, typically a polymer.

[0062] The socket 10 of the invention permits connection of baresemiconductor dice with very fine pitch bond pads to substrates, wherebyshort leads are used for improved performance. The semiconductor dicemay be readily replaced without debonding of wires or other leads.Multiple semiconductor dice may be simultaneously connected to asubstrate, and the apparatus permits high density “stacking” of a largenumber of dice. The socket uses leads which may be produced bywell-developed technology, and is easily made in large quantity and atlow cost.

[0063] It is apparent to those skilled in the art that various changesand modifications may be made to the bare die socket module of theinvention, sockets formed therefrom and methods of making and practicingthe invention as disclosed herein without departing from the spirit andscope of the invention as defined in the following claims. It isparticularly noted that with respect to numbers and dimensions ofelements, the illustrated constructions of the various embodiments ofthe modular bare semiconductor die socket are not presented as alimiting list of features but as examples of the many embodiments of theinvention.

What is claimed is:
 1. A bare semiconductor die interconnect socket forelectrical connection to traces of a substrate comprising: a pluralityof interconnect lead tapes, each interconnect lead tape having aplurality of leads; and at least two plates, each plate of said at leasttwo plates stacked in side-by-side relation connected to another plateof said at least two plates, two adjacent plates of said at least twoplates stacked in said side-by-side relation having a bare die insertionslot and a lead tape insertion slot; one interconnect lead tape of saidplurality of interconnect lead tapes being placed through said lead tapeinsertion slot between said two adjacent plates in said side-by-siderelation of said at least two plates.
 2. The socket of claim 1, whereina plate of said at least two plates is adhesively secured to an adjacentplate of said at least two plates.